The present invention relates generally to semiconductor processing and more particularly to a brush assembly for cleaning wafers.
Semiconductor manufacturing processes demand wafers, typically silicon wafers, which are substantially particulate free. As the semiconductor industry moves towards processing larger diameter wafers, for example 300 mm diameter wafers, it becomes increasingly difficult to remove particulates from the wafers. In particular, wafer cleaning processes must effectively remove particulates from the larger wafer surface area associated with the larger diameter wafers. Further, wafer cleaning processes must clean the wafers without exerting undue force on the wafers since larger diameter wafers have less mechanical strength than smaller diameter wafers.
In accordance with the present invention, a brush assembly includes a distributor having a slot matrix formed in an outer surface of the distributor, the slot matrix including a plurality of longitudinal slots intersecting a plurality of annular slots. The distributor is mounted on a hollow shaft having a plurality of perforations. The brush assembly further includes an outer housing having an inner surface abutting the outer surface of the distributor and a brush mounted on the housing.
During use, liquid flows from inside of the shaft through the shaft perforations to the distributor. The liquid then flows through a plurality of perforations in the distributor, one perforation being located in each longitudinal slot between adjacent annular slots. After flowing through the perforations in the distributor, the liquid flows through the longitudinal slots to the annular slots. The liquid then flows through the annular slots in the distributor to and through annular columns of perforations in the housing. The liquid flowing through the annular columns of perforations in the housing flushes the brush from the inside out.
Of importance, the flow of liquid from the shaft to the housing is readily controlled by appropriately selecting the dimensions of the longitudinal slots and annular slots in the distributor through which the liquid must flow. Generally, increasing the cross-sectional area and, to a lesser extent, decreasing the length of a slot increases the flow of liquid through the particular slot and vice versa. Thus, the flow of liquid from the shaft to the housing is readily controlled (restricted) by selecting the cross-sectional area of the longitudinal slots and annular slots of the distributor. As an illustration, a first distributor having longitudinal slots and annular slots with greater cross-sectional areas than those of a second distributor will allow a greater amount of liquid to flow from the shaft to the housing than the second distributor.
In one embodiment, the annular slots are formed closer together near the ends of the brush than in the center of the brush. As a result, a greater amount of liquid is provided to the ends of the brush than to the center. This is a particular advantage in wafer cleaning operations where a greater effective wafer surface area near the ends of the brush must be cleaned.
The distributor also restricts the liquid flow from the shaft to the housing. This allows the number of perforations in the housing to be increased without significantly increasing the overall amount of liquid used. This is particularly advantageous since increasing the number of perforations in the housing reduces localized nonuniform flushing of the brushes. Further, by restricting the flow of liquid, the distributor causes a uniform pressure buildup inside of the distributor. This, in turn, ensures that both ends of the brush receive the same amount of liquid and are uniformly flushed which improves particulate removal from the brush and reduces or eliminates uneven wear of the brush.
In accordance with the present invention, a method of removing particulates from a brush is provided. The method includes creating a liquid flow from a shaft to a housing, the brush being mounted on the housing. This liquid flow is redistributed by a distributor. In one embodiment, the liquid flow is redistributed to restrict the flow of liquid. In another embodiment, the liquid flow is redistributed to cause a greater amount of the liquid flow to flush the ends of the brush than the center of the brush.
These and other objects, features and advantages of the present invention will be more readily apparent from the detailed description of the various embodiments set forth below taken in conjunction with the accompanying drawings.